Begin by melting the butter in a saucepan over low heat until just melted. Transfer it to a bowl and allow it to cool to room temperature, typically about 15 minutes.

In a mixing bowl, combine the granulated sugar and fresh lemon zest, rubbing them together until the mixture resembles wet sand.

Add the cooled butter, whisking until fully incorporated. Next, add the egg and vanilla extract, stirring continuously until smoothly combined.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, poppy seeds, and salt. Gradually add this to the wet ingredients, mixing gently until just combined.

Using a cookie scoop, portion out the dough into equal-sized balls and place them on a lined baking sheet. Chill the cookie dough in the refrigerator for about 30 minutes.

Preheat your oven to 180ºC (355ºF) while your dough is chilling. Bake the cookies for 10-11 minutes until set at the edges and slightly soft in the center.

Once baked, leave them on the tray for 3 minutes before transferring to a cooling rack.

Prepare the cheesecake frosting by whipping together the cold cream cheese, vanilla extract, powdered sugar, agave or honey, and heavy cream until you achieve stiff peaks.

Once cookies are completely cool, use a piping bag to frost them generously with the cheesecake frosting, adding poppy seeds and lemon slices on top as desired.